The invention relates to a drive for an adjustment device inside a vehicle, and in particular to a drive for an adjustment device with a worm wheel having a globoid toothing with a cylindrical section.
A known drive for seat adjustment devices is described in EP 1 068 093 B1 and illustrated in FIG. 1. A seat of a vehicle (not shown) is fastened to a holding plate 1 which is coupled in turn to a top rail 3. A motor 2 is rigidly connected to the holding plate 1, and thus the top rail 3, with fastening lugs 10. A drive shaft 11 is located on both ends of the motor 2. The drive shaft 11 and a gear mechanism 9 define a connection detailed in EP 1 068 093 B1. The gear mechanism 9 sits within a U-shaped retaining bracket 8, where the retaining bracket 8 may be fastened to the top rail 3 through fastening holes 7.
The top rail 3 slides along a fixed bottom rail 4 fastened to a floor of the motor vehicle (not shown) either directly or indirectly through adjustment and/or bearing elements (not shown).
The top rail 3 and the bottom rail 4 are held by contact or support regions so as to create a cavity. A threaded spindle 5 is located within the cavity. The threaded spindle 5 is accommodated between retaining brackets 6 which are fixed to the bottom rail 4 by an appropriate bolt connection or an analogous fastener projecting through fastening holes in the retaining bracket 6 and bottom rail 4. Spindle 5 is screwed on to the retaining brackets 6 with appropriate fastening nuts.
FIG. 2 is a detailed illustration of the gear mechanism 9. The gear mechanism 9 comprises a drive worm 20 which is configured to engage an outer toothing of a worm wheel 30. The drive worm 20 is connected to the motor 2 through the drive shaft 11. The worm wheel 30 has an internal thread 32 which engages the threaded spindle 5. When the motor 2 turns, it transmits its motion through the drive shaft 11 to the drive worm 20. The drive worm transmits its rotational motion to the worm wheel 30. The worm wheel 30 propels the threaded spindle 5 which therefore moves the top rail 3 and the vehicle seat longitudinally.
As is shown in FIG. 2, the gear mechanism 9, which includes the drive worm 20 and the worm wheel 30, is located in a housing which is composed of four housing plates 14. The housing is situated within the U-shaped recess of a retaining bracket 8. Both the drive worm 20 and the worm wheel 30 have annular projections 21 and 31 respectively at their ends. The annular projections 21 and 31 are supported within corresponding openings in the housing plates 14. The individual housing plates 14 have bearing holes or bearing bushings 14a. Thrust washers 16 are seated on the annular projections 31 of worm wheel 30, while thrust washers 18 are seated on the annular projections 21 of the drive worm 20. The thrust washers 16 and 18 are particularly necessary to reduce wear between the bearings 14a and the cylindrical toothings on the ends of worm wheel 30.
In FIG. 3, the worm wheel 30 together with the cylindrical toothing 33 run helically relative to the A axis. The cylindrical helical toothing 33 has helically shaped and continuous tooth crowns 34 and tooth roots 35.
The toothing engagement between the cylindrical helical toothing 33 and the drive worm 20 is sensitive to any axial misalignment of the spindle nut caused by assembly, component tolerances, and/or wear of the individual components.
The toothing roots 35 of the toothing 33 extend to the end faces 37 of the worm wheel 30. This configuration may cause damage to the bearing bushings 14a in the housing plates 14 when the toothing roots 35 on the end faces 37 contact the bearing bushings 14a. To prevent damage to the bearing bushings 14a, thrust washers 16 are positioned over the annular projections 31 and against the end faces 37. The thrust washers typically have tabs 16a to engage in the toothing spaces of the cylindrical helical toothing 33 to prevent circumferential sliding.
However, the thrust washers 16 have various disadvantages. Due to the need for additional parts, they may increase the fabrication and assembly expense for this type of gear mechanism. In another example, thrust washers 16 produce undesirable noises. When these thrust washers 16 are used, for example, rattling noises and frictional noises are produced which are caused by deviations in concentricity and shaft-center-distance tolerances. In a further example, the axial play of the spindle nut within the housing is increased by the summation of individual tolerances.
There is a need for an improved drive with fewer components to reduce fabrication and assembly costs, while concurrently eliminating the noise problems.